1) Field of the Invention
The invention is in the field of X-ray Photoelectron Spectroscopy Analysis.
2) Description of Related Art
X-ray Photoelectron Spectroscopy (XPS) metrology commonly employs monochromatic aluminum Kα (AlKα) X-rays, which may be generated by bombarding an aluminum anode surface with a focused electron beam. A fraction of the generated AlKα X-rays is then intercepted by a focusing monochromator and a narrow X-ray energy band is focused onto the analysis site on a sample surface. The X-ray flux of the AlKα X-rays at the sample surface depends on the electron beam current, the thickness and integrity of the aluminum anode surface, and the stability of the monochromator. In general, the X-ray flux at the analysis site cannot easily be predicted with sub-percent precision. This may render calculations that include a value for X-ray flux insufficient in cases where the metrology requirements can be, e.g., 0.5% or less in error.
Typically, calculations using XPS measurements factor out the contribution of X-ray flux by using a ratio of two distinct XPS signals. For example, two different film thickness measurements may be used in a ratio, cancelling the X-ray flux value, in order to calculate the thickness of one of the two films. In such a calculation, one film is used as a known standard in analyzing the properties of the other film. However, it is not always the case that a sample readily includes a known standard quantity to which an unknown quantity may be calibrated. Furthermore, an XPS signal of a known standard quantity may have to be collected at a different time than the XPS signal for the unknown quantity. In that case, even though the contribution of X-ray flux is factored out of the calculation, the approach does not account for any changes in X-ray flux at the different times of collection of the XPS signals.
Thus, a method and a system for calibrating an XPS measurement are described herein.